Spinal discs comprise a central region called the nucleus pulposus surrounded by a second region known as the annulus fibrosis. The annulus portion comprises collagen fibers which may weaken, rupture, or tear, which limits annular confinement of the nucleus, producing disc bulges, herniations and other disc pathologies that cause nerve irritation or damage with resultant back pain and/or weakness and pain in the extremities.
In some open surgical treatment protocols, disc repair is attempted by removal of all or part of the damaged disc. Disc pathologies have also been treated with the application of heat to the disc. One such method is described in U.S. Pat. No. 5,433,739 to Sluijter et al. The method described in this document attempts to destroy or alter nerves at the disc surface by application of RF or direct current electrical energy to the center of the disc so as to heat the entire disc. Other approaches to heat based disc repair involve the heat induced shrinkage of the annulus fibrosis collagen. One instrument for performing such a treatment is described in U.S. Pat. Nos. 5,569,242 and 5,458,596 to Lax et al.
Existing methods of disc repair either ignore pathologies which are the true cause of patient pain and discomfort, or are apt to cause damage to the disc itself and/or adjacent structures. Improvements in disc repair methods and apparatus are thus needed.
The invention comprises methods of repairing intervertebral disc tears and fissures in a minimally invasive manner. In one embodiment, one or more expanding cannulas are used to access the desired disc so as to achieve direct visualization of the disc pathology. Fiber optics may be used to illuminate the field. In one embodiment method according to the invention comprises applying heat to a disc fissure while adjacent structures such as the nerve root and thecal sac are retracted away from the site. This minimizes thermal damage to tissues adjacent to the disc during the heating process. In an especially advantageous embodiment, the disc at the fissure is heated by placing a light absorbing dye such as indigo carmen or methylene blue in and around the fissure. Directing light from, for example, a laser light source, to the dye selectively heats the dye and thus the region of the fissure without affecting or damaging other parts of the disc such as the cartilaginous end plate. With direct visualization of the area, not only disc pathologies but bony and ligamentous pathologies can be addressed at the same time.
Although the posterior approach with fiber optic illumination is advantageous because the posterior section of the disc is the site of tears or fissures for most disc pathologies, visualization of fissures can also be obtained in an anterior or retroperitoneal approach with ultrasound imaging or imaging with optical coherence tomography.
Instrumentation for performing these methods is also provided. A high speed burr with a non-conductive foot plate for retraction can be guided to the site through the cannula and used to perform an internal laminoplasty, foraminotomy, or partial fasciectomy. Other instrumentation includes a nerve root retractor which is expandable in a cephalad and caudal direction by using a trigger on the handle. The retractor may have an angulating tip and an anchoring spike for hands free retraction. The retractor may also be provided with a lumen for suction and/or a lumen for fiber optic illumination. The retractor is preferably provided with a thermally and electrically nonconducting tip to avoid heat or electrical energy transfer from the fissure site to retracted tissues during the process of heating an annular fissure.